172 Evolution and Distribution of Fishes 



CHAPTER VI 



The Physical and Biological Environment of Fishes. 

 (c) During the Triassic-Jurassic Period. 



I. The Triassic Formation, like others already stud- 

 ied, can be fairly sharply divided into freshwater and ma- 

 rine beds. In Europe, the formation has been grouped 

 under four divisions : the lowest or Bunter, a higher or 

 Muschelkalk, a third the Keuper, and a highest or Rhaetlc. 

 Broadly it may be said that over the above region the lower 

 part of the Bunter, the lower Keuper or Lettenkohle, the 

 upper Keuper, and the Rhaetic were of freshwater origin. 

 The upper Bunter, the Muschelkalk, and occasional beds of 

 the Keuper were marine. But even in the often thick de- 

 posits of Muschelkalk rocks, strata are met with, that alike 

 by their plants and their freshwater animal remains, as by 

 their entire want of marine organisms, proclaim a temp- 

 orary elevation of land, and sub-aerial or freshwater de- 

 posits. 



The most exhaustive general treatment is that of Freeh 

 and collaborators {128). But their somewhat mixed and 

 diffuse treatment is only slightly helpful in an inquiry like 

 the present. For an accurate estimate of the varying life- 

 conditions of the period can only be reached from detailed 

 study of books or papers of individual authors. 



If one peruse the extensive lists of fossils given in 

 "Lethaea" for strata of the typical Upper Bunter, for the 

 Muschelkalk generally, and for various beds of the Keu- 

 per, one at once notes that the lists are wholly made up 

 of invertebrate and typically marine organisms, while ver- 

 tebrates are wholly absent. But to this are some exceptions. 

 Thus Wysogorski (/25: II pt. i : 55-57) gives from the 

 Lower Muschelkalk of Upper Silesia, a typical marine lot 

 in the Dadocrinus zone, but also a list of what suggest land 

 or freshwater animals including eight saurian reptiles, one 

 labyrinthodont (Capitosatirus) , also teeth, plates and 

 scraps of such fishes as Saurichthys latifrons, S. lepidosteus, 

 Colohodus chorzowensis, and C. gogolinensis. These 



